Forensic case: Several family members dwelling in homes of a village suffer from

Question

Forensic case: Several family members dwelling in homes of a village suffer from chromium(VI) intoxication. A nearby factory has been using chromium compounds for 30 years. Develop a sampling and analysis strategy to figure out whether or not Cr(VI) has been leaching from the property of the factory and reached the families. Take the following issues and facts into account:

a.The various chromium species behave very similarly in atomic spectroscopies including ICP.

b. Lawyers of the company running the factory will claim in court that any chromium found in the environment and properties may be the less toxic Cr(III), and the Cr(VI) in the victims came from somewhere else.

c. Solubility of chromates like Na2CrO4 and K2CrO4 is higher than 62 g/L.

d. Solubility product of chromium(III) hydroxide is 6.3x10-31 mol2/L2.

Explanation / Answer

Chemistry

Analysis

Solubilities of Na2CrO4 and K2CrO4 is very high as compare to chromium(III) hydroxide. So chromium(III) hydroxide will be precipate while Na2CrO4 and K2CrO4 are soluble in water. By filteration we separate Na2CrO4 and K2CrO4 and chromium(III) hydroxide. Solid or residue is chromium(III) hydroxide while in filterate we have Na2CrO4 and K2CrO4. We will proceed with filterate ie. Na2CrO4 and K2CrO4.

In an aqueous solution the chromate ion, CrO42-(aq), can be converted to the dichromate ion, Cr2O72-(aq), in acidic condition.The extent to which these reactions occur is dependent upon the concentration of the hydrogen ion, H+(aq), in the solution. The H+(aq) concentration can be increased by adding a source of H+(aq) - hydrochloric acid, HCl.  

chromate-dichromate (K2CrO4) equilibrium

2CrO42- + 2H+       H2O + Cr2O72-

Now we have dichromate with us which can be estimated mohr salt (ferrous ammonium sulphate) in acidic condition using diphenylamine as the internal indicator.

C r2O72- + 14H++ 6e- 2Cr3+ +7H2O

(Cr in +6 state) (Cr in +3 state)

[Fe2+ Fe3+ + e-] x6

C r2O72- + 14H++ 6Fe2+ 6Fe3+ + 2Cr3+ +7H2O

Normality of Chromate = Normality of dichromate

Normality of dichromate = Normality of Mohr salt x Volume of Mohr salt )/ Volume of Dichromate

Sample

1 Take a accurate amount of sample from factory as well from village home.(include both liquid and solid)

2. Filter both samples separately.

3. Acidify both samples with H2SO4. till yellow color convert into red color.

4. Tranfer accurate 10 ml of sample into conical flask add 10 ml of dil. H2SO4 add 2ml of Phosphoric acid and 2-3 drops of diphenylamine. Titrate it with standard Mohr salt solution prepare in acid medium (H2SO4) till a permanent blue color is obtain. Carry out for two more reading. Done for both sample

5. Do calculation part with normalities

If both sample contain chromates then it show that factory leaching from the property of the factory and reached the families.

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.